Force resistance devices for human muscular development have been known in the art for some time. These devices, also known as exercise and physical therapy devices, are employed for a variety of purposes. In some instances, the devices are designed to put the user into general overall muscular shape. In other instances, the devices are designed to concentrate upon a single group of muscles to strengthen that particular group. In other instances still, the purpose of the device is to strengthen or protect damaged tissue, or increase activity in a damaged area, to provide physical therapy.
With regard to devices for strengthening the hands and arms, several such devices are known. In some exercise equipment, the user sits against a back board and brings a pair of mechanical members together by forcing his elbows together. This specific action exercises some muscles of the arm and the chest.
In another technique, bar bells or free weights may be lifted by the user while the user is in a variety of positions. If the user is lying on his side, and attempts to rotate a bar bell from a position where his radius and ulna is parallel to the ground to a position where the radius and ulna is perpendicular to the ground, the user will not get an even workout. The axial force against which the humerus turns will give high resistance at the outset, and virtually zero resistance once the weight is brought to its highest position.
Likewise, if the user is sitting upright, and leans slightly to the right to pick a weight up from a horizontal surface, it may be beyond the range of movement of the arm. Even if the weight can be picked up, the resistance will be uneven. This is due to the law of sines and cosines which dictates the that the torque on the humerus will be a function of the angle of the radius and ulna with respect to the vertical gravitational pull of the earth.
This same principle holds true where the hand engages a handle attached to a cord under tensile force. As the radius and ulna rotate with respect to the humerus the same sine and cosine relationship dictate the torque force transmitted to the humerus. This uneven application of force can damage muscles and impede an even and healthy progression of development.
Further, where the muscles engage a force which is high at the first moment of movement, the muscles may strain the ligaments and become sprained. Although the total resistance and weight can be adjusted, the force application versus displacement will retain the same ungainly, uneven force characteristics.
Another problem with arm exercise equipment is its size, weight, and lack of portability. The arms are second only to the legs in the force that is required for proper development. Weights used to develop the arms, or machines which use the force of weights are of necessity heavy and difficult to transport. Most do not have the ability to adequately isolate on desired muscle groups. Portability can be a severe limitation on the utilization of an exercise device. Non-portability translates predominantly into use in one location, which due to the mobility of the users limits the occasion to use the exercise device.
Another disadvantage regarding commonly available exercise equipment for the arms, is the protection afforded the elbow. When the force is applied through the human hand, there is a competition between the engagement of two sets of muscles, namely those directing the radius and ulna, and those directing the humerus. In cases of high strain, the high force from one muscle group can transfer to another as the arm strains. This can cause the elbow to move suddenly as the muscle groups adjust to apply the maximum force to the hand. Such rapid and unexpected movement of the elbow can cause injury, not only by straining of the muscles in an unexpected force shift, but the elbow can become injured by striking surfaces nearby. The injury from elbow impact is particularly dangerous, and defeats the purpose for which exercise was sought.
Another disadvantage with commonly available equipment which encourages the humerus to rotate will usually encourage rotation about an axis which is significantly displaced from the axis of the humerus. In other cases, the movement is encouraged about an axis which is not even parallel with the axis of the humerus. In both of these cases the arm may be encouraged to move in a manner which presses the range of motion allowed by the bones of the arm. This can cause severe and long term damage to the joints.
In addition, no device has yet shown a good effectiveness in strengthening the muscles associated with angular displacement of the humerus along its axis, such as is required in arm wrestling. Arm wrestling requires a good grip, and adequate pectoral development, but is especially dependent upon the muscles which produce angular displacement of the humerus, along its axis. Presently available exercise equipment does not adequately focus upon this muscle group.
What is therefore needed is an exercise device which concentrates on the muscle groups which enable the humerus to move about its axis, or axis as closely as possible coaxial with respect to the humerus. The device should deliver a more even force versus displacement profile to evenly spread power throughout the angular displacement of the humerus. The needed device should be simple, light weight, and adjustable with regard to the opposing force. The needed device should not require special considerations to facilitate its use. The needed device should be utilizable with ordinary human surroundings and not require excessive space. The needed device should provide protection to the elbow and virtually eliminate the possibility of contact-type injury. The device should enable rotation of the humerus about an axis as close to the axis of the humerus, and as parallel to the axis of the humerus as possible.